Hydrocarbon sweetening process



Unite Stts This invention relates to a method for the direct sweetoning of hydrocarbon oils containing acidic sulfur compounds. More particularly, it relates to a method for converting acidic and malodorous mercaptans in petroleum hydrocarbon fractions into organic disulfides, and especially to such a method for the treatment of petroleum hydrocarbon fractions which contain a relatively small proportion of such undesirable sulfur compounds.

It is well known commercial practice to extract mercaptans from hydrocarbon oils by means of an aqueous solution of an alkali metal hydroxide and a solutizer, which is added to the hydroxide to increase its extractive power for mercaptans. Suitable alkali metal hydroxide solutions are aqueous sodium and aqueous potassium hydroxide solutions of varying concentrations, although preferably the concentration employed is 2-normal or higher, since higher concentrations tend to promote the extraction of mercaptans. Examples of suitable solutizers are amino and hydroxy alkyl amines in which the alkyl groups contain 2 or 3 carbon atoms, glycol-s, amino glycols and diamino glycols with from 3 to 5 carbon atoms, diamino, di-hydroxy or amino hydroxy dialkyl ethers or thioethers in which the alkyl groups contain 2 or 3 carbon atoms, alkali metal salts, in particular potassium salts, of fatty acids with from 3 to 5 carbon atoms, such as isobutyric acid, or of hydroxy or amino fatty acids with from 4 to 7 carbon atoms, or of phenyl acetic acid, or of hydroxy phenyl acetic acids or of amino phenyl acetic acids, alkyl phenolates, and mixtures of two or more of the aforementioned compounds.

Particularly suitable solutions are the aqueous solutions described in Ten Have, US. 2,763,594, issued September 18, 1956, of an alkali metal hydroxide and as solutizer a phenolate (which may be substituted by alkyl groups with a total quantity of not more than 3 carbon atoms and which contains no other substituents), containing not more than 54% by volume of water and not less than 2 moles per liter of free alkali metal hydroxide. The phenolate in these solutions increases both the extractive power for mercaptans and the dissolving power for oxygen. This method has been widely adopted in commercial practice because of its effectiveness and simplicity, especially in the sweetening of hydrocarbon fractions containing an amount of mercaptans insufficient to justify exensive mercaptan extraction processes wherein a large volume of extraction solution must be applied to the hydrocarbon oil and subsequently treated or regenerated in a separate step to remove the extracted mercaptans.

Although with the use of the latter compositions optimum results are obtained in the extraction of mercaptans from the hydrocarbon oil and in the subsequent oxidation of disulfides of the mercaptans taken up by the alkali metal hydroxide solution in certain cases, especially in the treatment of cracked products, dark coloration of the hy- Patented Sept. 11, 1962 drocarbon oil is found to occur as a secondary phenomenon.

Since consumers, especially in the case of at least some grades of gasolines, kerosenes, jet fuels, etc., usually require colorless, so-called water-white products, the above phenol-containing caustic alkali solutions cannot be used owing to their discoloration, especially as these coloring components cannot be removed from the hydrocarbon oil by a simple after-treatment.

It is therefore a principal object of the present invention to provide an improved process for the sweetening of hydrocarbon oils. Another important object is to provide an improved process for the conversion of mercaptans to disulfides in aqueous caustic solution. A further object is to provide an improved process for the conversion of mercaptans to disulfides by the use of an aqueous alkali metal hydroxide solution which can be easily and inexpensively regenerated. A still further object is to provide an improved process for the attainment of the foregoing objects without substantial degradation in the color of the sweetened hydrocarbon oil.

Subsequent research has shown that the above-mentioned dark coloration of the hydrocarbon oils is due to the oxidation of phenols to quinones which, together with mercaptans, can lead, in the presence of oxygen, to subsequent reactions to form dark oil-soluble compounds.

It has also been found that it is mainly the phenols with a somewhat higher molecular weight, such as phenols containing in the alkyl group or groups more than 3 carbon atoms, which by their ready oxidizability lead to the for mation of colored compounds. It might therefore have been expected that when phenols, containing in the alkyl group or groups not more than 3 carbon atoms, are used as solutizers according to the aforementioned Ten Have patent, there would be little or no discoloration of the hydrocrabon oils. This, however, is not the case, and it was possible to prove that the discoloration is caused by readily oxidizable alkyl phenols of a somewhat higher molecular Weight which naturally occur in certain hydrocarbon oils. In view of their boiling points these alkyl phenols mainly occur in hydrocarbon oil fractions boiling above the gasoline range, such as kerosene and jet fuels.

When, for example, a kerosene naturally containing such readily oxidizable alkyl phenols is brought into intimate contact with an alkali metal hydroxide solution containing as solutizer the less readily oxidizable phe nols with not more than 3 carbon atoms in the alkyl group or groups, the solutizer phenols are found to pass from the alkali metal hydroxide solution into the kerosene, and conversely, readily oxidizable alkyl phenol-s are transferred from the kerosene to the alkali metal hydroxide solution. The latter alkyl phenols are oxidized to disul fides in the alkali metal hydroxide solution by the free oxygen required for the oxidation of the mercaptans and the oxidation products then react to form colored, oilsoluble compounds which will again pass from the aqueous alkali metal hydroxide solution to the hydrocarbon oil.

Since the solutizer used in the aqueous alkali metal hydroxide solution serves to improve the extraction of the mercaptans from the hydrocarbon phase, it is obvious that an improvement of the mercaptan extraction will also effect an increased extraction of the alkyl phenols from the hydrocarbon oil. It might therefore be expected that generally all solutizers, for example those mentioned in the British patent specification No. 712,056, which serve to increase the extractive power for mercaptans, will show discoloration when the hydrocarbon oil to be treated contains readily oxidizable alkyl phenols.

It has now been found that there is little or no discoloration of hydrocarbon oils containing alkyl phenols with the use of a combination of a formic acid salt and an auxiliary substance for promoting the solvent power for oxygen.

The invention therefore relates to a process for the preparation of a colorless or substantially colorless light hydrocarbon oil freed or substantially freed from mercaptans by contacting a light hydrocarbon oil containing mercaptans, in the presence of oxygen, with an aqueous alkali metal hydroxide solution, which process is characterized in that an aqueous alkali metal hydroxide solution is used which contains a combination of a formic acid salt as solutizer to increase the extractive power for mercaptans and an auxiliary substance for promoting the solvent power for oxygen.

Hitherto it was thought that for a rapid conversion of the mercaptans present in hydrocarbon oils it was necessary to employ in the alkali metal hydroxide solution solutizers which increase as far a possible the extractive power of the solution for mercaptans. The underlying idea was that with high concentrations of mercaptides in the aqueous caustic alkali phase the mercaptides would be rapidly oxidized to disulfides.

The invention is based on the unexepected finding that for a rapid and effective conversion of the mercaptans present in hydrocarbon oils it is unnecessary to use in the alkali metal hydroxide solution such particularly active solutizers for increasing the extractive power for mercaptans, and that a solutizer is suflicient which only increases to a comparatively slight degree the extractive power for mercaptans when this solutizer is combined with an auxiliary substance which promotes the solvent power for oxygen. Surprisingly it has also been found that with the use of this combination there is little or no discoloration of the hydrocarbon oil.

Formic acid salts, especially the alkali metal salts thereof, are suitable as solutizers which only increase to a comparatively slight degree the extractive power for mercaptans. An advantage of these salts is that they are commercially available to an unlimited extent at a low price, unlike the solutizers previously used which are usually considerably more expensive and moreover are often impossible to supply in a sufficiently pure form.

Suitable auxiliary substances which promote the solvent power for oxygen are organic compounds consisting only of carbon, hydrogen, and oxygen, containing at least one alcoholic hydroxyl group per molecule and which are soluble in an aqueous alkali metal hydroxide solution, or mixtures of such compounds. Particularly suitable are monohydric or polyhydric alcohols, containing up to carbon atoms per molecule, which may also contain one or more ether groups and/ or carboxyl groups, or mixtures thereof. It is preferred that the auxiliary substance contain no more than 5 oxygen atoms. Dihydric and/ or trihydric alcohols having from 2 to 6 carbon atoms per molecule are especially suitable, particularly the polyalkylene oxide ether-alcohols within this class and most especially diethylene glycol and triethylene glycol. As examples may be mentioned methylene glycol, diethylene glycol, triethylene glycol, glycerine and mixtures thereof. Suitable alcohols containing ether groups are, for example, the products marketed under the trade names of methyl Cellosolve and ethyl Cellosolve, i.e., the monomethyl and monoethyl ethers, respectively, of ethylene glycol (see L. F. Fieser and M. Fieser, Organic Chemistry 1950), 2nd edition, page 124). Suitable alcohols containing carboxyl groups are, for example, tartaric acid, gluconic acid and hydroxybutyric acid.

The concentration in which the combination of the auxiliary substances is used in the aqueous alkali metal hydroxide solution may vary within wide limits and is generally between 10-65% by weight, although concentrations of 40-60% by weight are preferred.

In the combination of the auxiliary substances the relative weight ratio of the auxiliary substance for promoting the solvent power for oxygen to the formic salt generally varies from about 3:1 to about 1:3 and is preferably from about 1:2 to about 1:2.5.

The ratio of the volume of the aqueous alkali metal hydroxide solution containing the solutizer to the volume of the hydrocarbon oil will generally vary from about 0.05 to 5 and preferably lies between 0.1 and 1.

The concentration of free alkali metal hydroxide in the aqueous solutions is generally 1 to 20% by weight and preferably lies between 14 and 17% by weight. The alkali metal hydroxide used in the process of the invention is preferably either sodium hydroxide or potassium hydroxide. Potassium hydroxide is particularly preferred because of the lower viscosity of solutions thereof at the concentrations required in the process.

The present process for converting mercaptans into disulfides is generally carried out at temperatures of 0 to 70 C., although temperatures outside this range may also be applied, if desired. The temperature range of 15 C. to 55 C. is preferred. It should be borne in mind that sudden drops in temperature of the alkali metal hydroxide solution should be avoided since in this case there is a risk of a second liquid alkali phase forming, or of solid components crystallizing out from the solution.

The oxygen required for the process may be supplied either as such or as a mixture of oxygen with another gas that is inert under the operating conditions, e.g., in the form of air, which is particularly suitable.

The oxygen may be dissolved in the hydrocarbon oil in advance or be injected into the hydrocarbon oil while the latter is being brought into contact with the aqueous solution of an alkali metal hydroxide and the solutizer combination. The quantity of oxygen should at least be equivalent to the quantity of mercaptans to be oxidized. It is preferred to use an excess of 50 to 200% and more, and more particularly of to calculated on the quantity of oxygen theoretically required.

If the process is used for removing mercaptans from gasoline or kerosene with a content of mercaptan sulfur not exceeding approximately 0.02% by weight and the gasoline or kerosene is in equilibrium with the atmosphere, the quantity of oxygen present in the gasoline or kerosene is generally suflicient to effect the desired oxidation. However, the process for removing mercaptans from gasoline and kerosene is frequently carried out shortly after the gasoline or kerosene has been produced from the crude oil, and after any other pretreatments have been carried out, with the result that it is not saturated with air. In that case it is necessary to dissolve air or another oxygencontaining gas in the hydrocarbon oil before or during contact with the caustic alkali solution.

In general, the present process is carried out under atmospheric pressure. If the process is used for removing mercaptans from hydrocarbon oils with a comparatively high content of mercaptans, for instance, a mercaptan sulfur content of 0.04% to 0.05% by weight or more, using air as oxygen-containing gas, it may be advisable to operate under elevated pressure in order to dissollve an adequate amount of oxygen in the hydrocarbon o1 The action of the oxygen may be promoted by the simultaneous use of a peroxide in an amount of 10 to 40% and more particularly of 15 to 25% of the stoichiometric amount with respect to the mercaptans to be converted, so that in this case the use of excess oxygen is not re quired.

This has certain advantages, especially when hydrocarbons with a relatively high content of mercaptan sulfur are treated and increased pressure is required in order to dissolve the necessary amount of oxygen in the hydrocarbon oil, since when the pressure is released there is a certain loss of hydrocarbon oil by evaporation.

In order to promote the transfer of the oxygen from the hydrocarbon phase to the caustic alkali phase in which the oxidation proper takes place, care should be taken to effect an intimate contact between the two phases. This contact can be brought about in various ways, for instance by means of a centrifugal mixer or a propeller mixer. The mechanical power transferred from the stirrer elements to the mixture of the two phases in the mixer should be at least 0.1 kw. per cubic meter of mixture.

A suitable centrifugal mixer is the so-called Turbo mixer (see John H. Perry, Chemical Engineers Handbook, 1941, pp. 1554-1555).

The desired contact between the oil and caustic alkali phase may also be effected by spraying the caustic alkali solution very finely under high pressure, for instance, by means of a spray nozzle, into the hydrocarbon oil or, conversely, by spraying the hydrocarbon oil into the canstic alkali solution in this manner.

The various means customarily employed in extraction processes for increasing the surface of contact between the phase to be extracted and the extraction agent may also be used for the present purpose. Thus the process may be carried out in a column provided with packing units, perforated plates, projections or rotating discs. The hydrocarbon phase and the caustic phase may be passed through the column in concurrent flow or in countercurrent flow.

When the two phases are passed upwards and in concurrent flow through columns (for example as described in the British patent specification No. 759,560 in the case of a column provided with packing units), a dispersion of the oil-in-water type may be obtained even if the quantity of the aqueous alkali metal hydroxide solution conducted through the column per unit of time is much smaller than the quantity of hydrocarbon oil, since under the stationary conditions existing at points situated comparatively close to the bottom of the column, the ratio of the volume of alkali metal hydroxide solution present to the volume of hydrocarbon oil present is greater than the ratio in which the two phases are supplied to the column. When, for example, the ratio of the volume of hydrocarbon oil supplied to the volume of aqueous alkali metal hydroxide solution supplied lies between 1011 and 3:1, in a large part of the column the ratio of the volume of hydrocarbon oil present to the volume of aqueous alkali metal hydroxide solution present may be about 1:1 after the stationary state has been reached.

Not only does the fine dispersion formed of the hydrocarbon oil in the aqueous alkali metal hydroxide solution greatly promote the transfer of oxygen from the hydrocarbon oil to the aqueous alkali metal hydroxide solution, but the nature of the dispersion also has the advantage that, after discharge from the column, it is easily separated into the two phases, the hydrocarbon oil separated containing no traces of the aqueous alkali metal hydroxide solution, which would be the case with separation of a dispersion of the opposite type, i.e., in which the aqueous alkali metal hydroxide solution has been dispersed in the hydrocarbon oil.

The present process provides a very simple method by which light hydrocarbon oils can be freed from mercaptans in a short period, which in many cases varies between 2 and minutes. If the hydrocarbon oil contains mercaptans which are difficult to oxidize, it may be necessary to keep the oil and the aqueous solution of the alkali metal hydroxide and the combination of auxiliary substances in contact with each other in the manner described for a somewhat longer period. On sufiiciently intensive contact between the hydrocarbon oil to be treated and the aqueous solution of alkali metal hydroxide and combination of auxiliary substances it is, however, also possible in the latter case to free the hydrocarbon oil from mercap- 6 tans to such an extent that the oil has a negative doctor test within one hour.

After the hydrocarbon oil and the aqueous alkali metal hydroxide solution have been in contact with each other for a suificiently long time they are separated from each other.

The process may be carried out either continuously or batchwise.

When the process is carried out batchwise the entire quantity of hydrocarbon oil and aqueous alkali metal hydroxide solution, which have been in contact with each other, is allowed to settle until the phases have separated from each other, which occurs after a short time.

When carrying out the process continuously, the hydrocarbon oil may be supplied to the aqueous solution of the alkali metal hydroxide in such a manner that the oil is in contact with the aqueous solution for a sufficiently long time and the continuously discharged hydrocarbon oil is passed into a separate settling vessel in which the entrained aqueous solution of alkali metal hydroxide separates out. The aqueous solution separated is as such suitable for treating a fresh quantity of hydrocarbon oil, since the mercaptans transfer only temporarily in the form of mercaptides in the aqueous solution of alkali metal hydroxide, and the disulfides formed during oxidation dissolve again in the hydrocarbon oil so that essentially no contaminations accumulate. in the aqueous solution of alkali metal hydroxide.

The process may be used for removing mercaptans from light hydrocarbon oils (i.e. hydrocarbon oils with a boiling point or end boiling point which is not higher than 350 C.), particularly kerosenes and gasolines of different origin containing alkyl phenols. The gasolines and kerosenes may be obtained either by straight distillation from crude oils or from heavier base materials by cracking.

An example of a hydrocarbon oil with a low phenol content 0.01% by weight) is straight-run gasoline having a final boiling point below about C. Generally speaking, reformed gasolines also have a low phenol content. Straight-run products having a boiling range of 150275 C., such as kerosene and jet fuels, generally have a phenol content of (ml-0.03% by weight. Gasolines, kerosenes, etc., obtained from higher hydrocarbon oils by thermal cracking, generally have a relatively high phenol content, for example 0.04-0.05 by weight or higher. Gasolines, kerosenes, etc., obtained from higher hydrocarbon oils by catalytic cracking also frequently have such a high phenol content.

It is preferred to remove from the hydrocarbon oils any acids present, such as hydrogen sulfide, which are stronger than the mercaptans, by means of a diluted aqueous alkali metal hydroxide solution before removing the mercaptans according to the process of the present invention. A pretreatment with dilute caustic alkali solution has the additional advantage that aromatic mercaptans, which on the one hand possess a considerably stronger acidic character than aliphatic mercaptans and which on the other hand are more difficult to oxidize than aliphatic mercaptans, are removed, at least in a considerable quantity, from the hydrocarbon oil to be treated in the manner described. Since aromatic mercaptans occur especially in light hydrocarbon oils obtained by cracking heavier hydrocarbons and particularly in products obtained by catalytic cracking, a pretreatment with diluted caustic alkali solution is especially suitable for such products. It is preferable to carry out this pretreatrnent before the cracked products come into contact with oxygen or an oxygen-containing gas so as to prevent gum formation.

Since, when applying the process of the invention for removing mercaptans from hydrocarbon oils, the disulfides formed during oxidation pass again into the hydrocarbon oil, the process is primarily suitable for treating hydrocarbon oils with a low mercaptan content, i.e. lower than 0.05% by weight, and preferably lower than 0.02% by weight, calculated as mercaptan sulfur. In this case it is obvious that the quantity of disulfides returned into the hydrocarbon oil is also small.

When a hydrocarbon oil with a considerable mercaptan sulfur content, for instance 0.05% by weight or more, is to be freed from mercaptans, it is possible first to remove the greater portion of the mercaptans, if desired together with other sulfur compounds, by any of the usual methods hitherto employed for the purpose and then to oxidize any remaining mercaptans by the process of the invention. The pretreatment for removing the greater portion of the mercaptans may, for instance, be effected by extracting (without oxidation) the hydrocarbon oil with an aqueous alkali metal hydroxide solution containing the combination of auxiliary substances according to the invention.

The resultant alkali metal hydroxide solution which contains mercaptans may be regenerated by treating this solution with oxygen or an oxygen-containing gas preferably in the presence of a light hydrocarbon oil, the ratio of the volume of the aqueous alkali metal hydroxide solution to the volume of the hydrocarbon oil being preferably between 0.2 and 5, and more particularly between 0.5 and 2.

cresols (mixture of the 3 isomeric cresols) were added as solutizer to improve the extraction of mercaptans;

(2) An aqueous potassium hydroxide solution to which a combination of formic acid and triethylene glycol was added as auxiliary substances.

Each of these tests was carried out until the recycling aqueous potassium hydroxide solution had a constant composition since the fresh solutions extract the mercaptans from the kerosene, but alkyl phenols are extracted from the kerosene as well. A proper assessment of the discoloration cannot be made until, as described above, the aqueous caustic solution has an equilibrium composition.

The results of the two continuous tests are assembled in the following table which also shows the equilibrium composition of the potassium hydroxide solution.

The analyses of the kerosene experiments show that under comparable conditions the same mercaptan removal was obtained, but that in the case of the alkyl phenol solutizer the color of the kerosene was considerably impaired and reduced from +30 to +1, whereas there was only a comparatively slight deterioration in the color, viz, from +30 to +23 with the use of the combination of formic acid and triethylene glycol.

Table Equilibrium Composition of the Aqueous KOH Analysis Solution Mercaptan Sul- Contact Product fur Content, Saybolt Color Time in Treated Alkyl Formie 'lri- Percent by Mixer in KOH, Phenols, Acid, ethylene Water, \vt.) Minutes g./l. g./l. g./l. Gly/clol, g./l.

Feed Product Feed Product Treated Treated Kerosene..- 184 434 382 112 9 +1 9 150-250 0.--- 419 27 218 139 107 112 0 +30 +23 9 When the process is applied to hydrocarbon oils ob- EXAMPLE The starting material used was a straightrun kerosene with a boiling range of from 150 to 250 C. (ASTM). This kerosene contained 0.0l66% by weight of mercaptan sulfur, 0.024% by weight of alkyl phenols and had a Saybolt color of +30.

The gasoline was pretreated with a dilute aqueous sodium hydroxide solution in the absence of oxygen in order to remove the acid components. The gasoline thus pretreated contained 0.02% by weight of mercaptan sulfur and 0.024% by weight of alkyl phenols and had a Saybolt color of +30.

The kerosene was continuously passed into a Turbo mixer at a temperature of 20 C. in a quantity of liters per hour, the impeller speed being 400 r.p.m. An aqueous potassium hydroxide solution containing a solutizer was also continuously supplied to the Turbo mixer at the rate of 20 liters per hour. In addition, air was blown into the kerosene supply line in a quantity corresponding to 200% of the quantity of oxygen theoretically required for the oxidation of the mercaptans present.

The mixture of kerosene and aqueous solution discharged from the mixer was passed into a settling space in which the two phases separated. The kerosene was discharged and the aqueous solution was recycled to the mixer.

In this way two continuous tests were carried out in which the aqueous solutions used were:

(1) An aqueous potassium hydroxide solution in which I claim as my invention:

1. A process for the preparation of a substantially colorless light hydrocarbon oil substantially freed from mercaptans which comprises contacting a light mercaptancontaining hydrocarbon oil in the presence of oxygen with an aqueous alkali metal hydroxide solution consisting essentially of a uniphase combination of alkyl phenols substantially identical with and in equilibrium with those naturally occurring in the light hydrocarbon oil, an alkali metal formate as solutizer to increase the extractive power of the solution for mercaptans and a polyfunctional organic compound which consists only of carbon, hydrogen, and oxygen, containing one alcoholic hydroxyl and at least one other functional group selected from the group consisting of ether, carboxyl and hydroxyl radicals and is further characterized in that it is soluble in the alkali metal hydroxide solution as an auxiliary substance for promoting the solvent power of the solution for oxygen.

2. The process of claim 1, wherein the formate used is potassium formate.

3. The process of claim 1, wherein the organic compound used as an auxiliary substance for promoting the solvent power for oxygen contains from 1 to 10 carbon atoms per molecule.

4. The process of claim 3 wherein the organic compound used as an auxiliary substance for promoting the solvent power for oxygen is a polyhydric alcohol selected from the group consisting of dihydric and trihydric alcohols.

5. The process of claim 4 in which the organic auxiliary substance contains from 2 to 6 carbon atoms per molecule.

6. The process of claim 1 in which the concentration of the combination of solutizer and organic auxiliary substance in the alkali metal hydroxide solution is from 10 to 65% by weight.

7. The process of claim 1 in which the ratio by weight of the organic auxiliary substance to the solutizer is from 3:1 to 1:3.

8. The process of claim 1 in which the ratio of the volume of aqueous alkali metal hydroxide solution containing the solutizer and organic auxiliary substance to the volume of hydrocarbon oil is from 0.05:1 to 5:1.

9. The process of claim 1 in which the concentration of free alkali metal hydroxide in the aqueous metal hydroxide solution is from 1 to 20% by weight.

10. The process of claim 1 in which the light hydrocarbon oil to be treated has a boiling range of from 10 about 150 to about 275 C. and has a phenol content exceeding 0.01% by weight.

References Cited in the file of this patent UNITED STATES PATENTS 2,223,798 Yabrofi et a1. Dec. 3, 1940 2,316,753 Ayers et a1. Apr. 20, 1943 2,585,284 Tom et a1. Feb. 12, 1952 2,850,434 Brooks et a1 Sept. 2, 1958 10 2,978,404 Bowers Apr. 4, 1961 

1. A PROCESS FOR THE PREPARATION OF A SUBSTANTIALLY COLORLESS LIGHT HYDROCARBON OIL SUBSTANTIALLY FREED FROM MERCAPTANTS WHICH COMPRISES CONTACTING A LIGHT MERCAPTANCONTAINING HYDROCARBON OIL IN THE PRESENCE OF OXYGEN WITH AN AQUEOUS ALKALI METAL HYDROXIDE SOLUTION CONSISTING ESSENTIALLY OF A UNIPHASE COMBINATION OF ALKYL PHENOLS SUBSTANTIALLY IDENTIAL WITH AND IN EQUILIBRIUM WITH THOSE NATURALLY OCCURING IN THE LIGHT HYDROCARBON OIL, AN ALKALI METAL FORMATE AS SOLUTIZER TO INCREASE THE EXTRACTIVE POWER OF THE SOLUTION FOR MERCAPTANS AND A POLYFUNCTIONAL ORGANIC COMPOUND WHICH CONSISTS ONLY OF CARBON, HYDROGEN, AND OXYGEN, CONTAINING ONE ALCOHOLIC HYDROXYL AND AT LEAST ONE OTHER FUNCTIONAL GROUP SELECTED FROM THE GROUP CONSISTING OF ETHER, CARBOXYL AND HYDROXYL RADICALS AND IS FURTHER CHARACTERIZED IN THAT IT IS SOLUBLE IN THE ALKALI METAL HYDROXIDE SOLUTION AS AN AUXILIARY SUBSTANCE FOR PROMOTING THE SOLVENT POWER OF THE SOLUTION FOR OXYGEN. 